Heat recoverable sleeves have found wide utility in many applications. Thus, heat recoverable sleeves are used as insulators for electrical conductors, particularly at areas where splices are formed in the electrical conductors. The sleeves have been particularly successful because they allow rapid and uniform application of an insulating covering. Typically, an electrical conductor which is to be spliced or repaired first has an expanded heat recoverable sleeve placed over the conductor. The repair is then made and the sleeve is put in place over the splice and recovered by the application of heat. Such methods have proven to be quicker, more convenient, and more reliable than prior methods such as taping and vulcanizing.
A disadvantage in use of heat recoverable sleeves is that a heat source is necessary for the recovery. Suitable heat sources include torches and hot air guns. In some cases, it is undesirable to use torches because of the danger of fire being started by the open flame. In other situations, working conditions are so cramped or otherwise difficult that it is not convenient to place a heat source such as a torch or heat gun close to the sleeve which is to be recovered. The use of heat-recoverable sleeves may also be undesirable where the substrate on which the sleeve is to be shrunk is temperature sensitive.
Various methods of recovering sleeves without the application of heat have been proposed. In particular, various types of expanded sleeves with internal restraints holding the sleeves in the expanded condition have been disclosed. One such sleeve comprises an expanded sleeve held in the expanded state by a cylinder of ice as disclosed in U.S. Pat. No. 3,319,328. In actuality, such a sleeve is also a heat-recoverable sleeve because it requires a minimal amount of heat to melt the ice and allow the sleeve to recover. However, the heat necessary is so low that such a sleeve is not normally considered a sleeve requiring an application of an outside heat source. Another type of sleeve having an internal restraint is that described in U.S. Pat. No. 3,515,798 wherein a rigid removable mechanical insert holds the sleeve in the expanded condition until the insert is removed.
In general, all of the proposals for making recoverable sleeves which do not require heat have involved internal restraints, configurations which place a restraint between the substrate and the internal surface of the sleeve or involve contacting the internal surface of the sleeve with some foreign material. Such configurations present various problems.
Frequently, it is desired to coat the inner surface of a recoverable sleeve with a sealant or adhesive material. Configurations of heat recoverable sleeves with internal restraints often make the use of such a coating difficult or impossible. Furthermore, the imposition of an internal restraint between the sleeve and substrate makes fitting of the sleeve over the substrate difficult and reduces the range of substrate sizes which the sleeve can be fitted over.